Drug addiction is a serious and costly disorder that is poorly understood with few effective treatments. Although animal models have begun to provide important information about some aspects of the neurobiology of addiction, an understanding of the basic molecular foundations of addiction remains elusive. Basic research with invertebrates has provided ground-breaking discoveries in uncovering the underlying mechanisms of behaviors as complex as learning and memory. Recent work indicates that the same basic types of behavior that define drug reward in mammals are also evident in invertebrates (crayfish, flies, c-elegans). C. elegans is an excellent model to study the neurobiological basis o human behavior with: a surprisingly conserved, fully sequenced genome that can be easily manipulated; a completely mapped neuroanatomical system; and a short generation time with low maintenance costs for fast generation of data at a fraction of the cost of many other organisms. C. elegans demonstrate movement toward, and concentration- dependent self-exposure to, various psychoactive drugs including cocaine, methamphetamine, ethanol and caffeine. We have found that they also show sensitization, tolerance, cross-sensitization, and cross tolerance after drug pre-exposure. In addition, we have recently reported that C. elegans display a conditioned preference for cues (salts) that had previously been paired with cocaine or methamphetamine which is analogous to findings in mammalian models of drug reward. Together these data indicate that C. elegans can serve as an excellent behavioral model system to study drugs of abuse with tremendous potential to uncover the underlying molecular foundations of addictions. However, clear behavioral evidence is needed to fully establish the C. elegans model and confirm that the phenomena observed thus far are consistent with findings in mammals. The current application will systematically examine the cue-conditioned preference response (CR) to cues previously associated with cocaine or methamphetamine to determine if some key characteristics present in mammals are also present in C. elegans. We will determine if the CR to stimulants in C. elegans shows persistence, extinction, and reinstatement, and if it i affected by conditioning trial frequency, drug pre- exposure, and/or food restriction. All of these characteristics are important factors in models of drug reward in mammals and are expected to also be present in C. elegans. In addition, we also propose to scale-down the behavioral assays to conduct them in six-well plates to enable fully objective, high throughput measurements of drug preference and cue-CRs using C. elegans. Follow-up studies would test mutant C. elegans strains with deficits in homologous genes in mammals that have been shown to mediate cue-CRs to drugs of abuse, and findings would be confirmed in wild-type worms using pharmacology, and/or RNAi technology. The establishment of a new behavioral model of addictions in C. elegans would be a transformational advancement in the field. Future studies would leverage the tremendous advantages of studying the mechanisms that underpin these behaviors in C. elegans. With the prospect of identifying new molecular targets, and the future application of this model to screen compounds for medications development, this project has a tremendous potential impact for the treatment of human drug addiction.